This invention relates to a sensor for measuring changes in ambient conditions as well as detecting contact between two objects.
Sensors are used to measure a variety of different physical properties, of which temperature and pressure are probably the most relevant to everyday life. Temperature sensors are used in a wide variety of-applications, including, inter alia, sensing the temperature of a fluid in a system, sensing the temperature of industrial processes, and sensing the temperature of electronic components to prevent overheating.
Pressure sensors are also used in a wide variety of applications including, inter alia, sensing the weight of an object, sensing the strength of an impact between two objects and sensing the pressure exerted by a fluid in a system. For example, a pressure sensor is utilized in all scales, which measure weight. Furthermore, scale-type pressure sensors can be used to detect the presence or absence of an object on the scale. For example, it would be advantageous to be able to detect the presence or absence of a person occupying the passenger seat in an automobile. This information could be used in a crash to determine which air bags to deploy and with how much force to deploy the air bags.
Pressure sensors are also an important part of testing the strength of objects. For example, consumer products under go significant testing to make sure that they can withstand the types of forces normally associated with their use.
Furthermore pressure sensors are used to sense the presence of fluids, either liquids or gases, in a system. For example, automobiles use a variety of fluids that allow the vehicle to operate such as motor oil, transmission fluid, antifreeze, and the like. The pressure of these fluids must be monitored to insure that sufficient fluids are present, while also insuring that damage to the vehicle is not caused by over pressurization of the fluid system. Another example of fluid pressure in an automobile that must be by monitored is air pressure in tires. Incorrect tire pressure can lead to tires that prematurely wear out and/or crashes from severely over or under inflated tires.
A subset of pressure sensors are those that detect contact between two objects.
Known temperature and pressure sensors have become unsatisfactory because of the manufacturing processes are complex and therefore expensive. Known sensors may include several moving parts, which need to be assembled. For many sensors, assembly of the moving parts requires precision because of their small size. The required high precision can also lead to high failure rates of the production process, leading to significant costs associated with wasted components. In addition, gas and liquid tight hermetically sealed sensors are particularly difficult and expensive to manufacture. Many failures of sensors and switching devices are do to excessive moisture and/or condensation. Sensors that are rugged, able to withstand high gravitationally forces and/or shock and hermetically sealed are extremely difficult to manufacture.
Accordingly, the inventor has recognized the need for a new type of sensor, which may be inexpensively and reliably manufactured.
A first aspect of the present invention relates to a temperature and/or pressure sensor that includes a first conductor connected to a source terminal and a second conductor connected to a return terminal. Between the two conductors resides a semi-conductive layer with a predetermined resistance. A resistance measurement device determines how the predetermined resistance of the semi-conductive layer changes in response to a change in pressure or temperature. Also included is a sensor with integral fault detection. The present invention also relates more generally to a coaxial cable, which includes a semi-conductive layer between two conductors. The present invention also incorporates a method of sensing pressure or temperature by measuring a change in resistance of a semi-conductive layer.
A second aspect of the present invention also relates to a contact sensor that detects contact between two objects. In this aspect of the invention, the first conductor is separated from the second conductor by a crushable layer with a predetermined crush resistance. The crushable layer deforms under pressure such that a signal passes between the first and second conductor.